ABSTRACTCarvedilol (CAR) is a potent antihypertensive drug but has poor oral bioavailability (24%). A nanosuspension suitable for pulmonary delivery to enhance bioavailability and bypass first-pass metabolism of CAR could be advantageous. Accordingly, the aim of this work was to prepare CAR nanosuspensions and to use artificial neural networks associated with genetic algorithm to model and optimize the formulations. The optimized nanosuspension was lyophilized to obtain dry powder suitable for inhalation. However, respirable particles must have a diameter of 1-5 µm in order to deposit in the lungs. Hence, mannitol was used during lyophilization for cryoprotection and to act as a coarse carrier for nanoparticles in order to deliver them into their desired destination. The bottom-up technique was adopted for nanosuspension formulation using Pluronic stabilizers (F127, F68, and P123) combined with sodium deoxycholate at 1:1 weight ratio, at three levels with two drug loads and two aqueous to organic phase volume ratios. The drug crystallinity was studied using differential scanning calorimetry and powder X-ray diffractometry. The in vitro emitted doses of CAR were evaluated using a dry powder inhaler sampling apparatus and the aerodynamic characteristics were evaluated using an Andersen MKII cascade impactor. The artificial neural networks results showed that Pluronic F127 was the optimum stabilizer based on the desired particle size, polydispersity index, and zeta potential. Results of differential scanning calorimetry combined with powder X-ray diffractometry showed that CAR crystallinity was observed in the lyophilized nanosuspension. The aerodynamic characteristics of the optimized lyophilized nanosuspension demonstrated significantly higher percentage of total emitted dose (89.70%) and smaller mass median aerodynamic diameter (2.80 µm) compared with coarse drug powder (73.60% and 4.20 µm, respectively). In summary, the above strategy confirmed the applicability of formulating CAR in the form of nanoparticles loaded on a coarse carrier suitable for inhalation delivery.

Mentions:
The relationships between the independent and dependent variables were summarized by the model in 3D response surface plots demonstrating the effects of two independent variables at average levels of other variables on the output parameters (Figures 1–3). The results of response surface plots showed that the most effective formulation variables that directly affect the PS of the nanosuspensions included stabilizer type, number of PPO units, weight of stabilizer, and the ratio of hydrophilic to hydrophobic units (Figure 1). The effect of the type of stabilizer on PS can be explained by the response surface plot (Figure 1A) showing that the PS values were low at stabilizer type 1 (Pluronic F127), high at stabilizer type 2 (Pluronic F68), and low at stabilizer type 3 (Pluronic P123). The ratio of hydrophilic to hydrophobic units (PEO/PPO) demonstrated increasing effects on PS moving from 0.55 to 3.05 and finally to 5.07 corresponding to Pluronics P123, F127, and F68, respectively (Figure 1B). However, the increase in PPO units from 30 (F68) through 65 (F127) and finally to 69 (P123) was found to have prominent decreasing effect on the PS, which is consistent with the effects of stabilizer type. Also, the increased weight of stabilizer led to a decrease in the size (Figure 1C). The drug to stabilizer ratio and phase volume ratio were found to have increasing and decreasing effects on PS, respectively (Figure 1D). The decrease in PS with increased levels of phase volume ratio might be due to the formation of more nucleation sites per unit volume of the antisolvent (aqueous phase). This caused the precipitation of less drug molecules per nucleation site and consequently decreased PS.46 Moreover, the decrease in PS with an increased weight of stabilizer could be attributed to the decrease in surface tension, which facilitated the size reduction and stabilized the formed nanoparticles with inhibition of aggregation.27 It is well known that the conformation of physically adsorbed triblock copolymers (Pluronics) depends on the hydrophobicity of the sorbent surface.47 The hydrophobic PPO block anchors to the hydrophobic surface, leaving the PEO chains extending in the aqueous phase, and when the number of the adsorbed polymeric chains is sufficiently high, a brush conformation is formed.47,48 The adsorption of a series of Pluronics on polystyrene colloids was studied to probe the effect of PEO chain length and the hydrophilic/hydrophobic block length ratio on the adsorption characteristics.49 It was found that the surface concentration of Pluronics on polystyrene colloids is determined by the size of the hydrophobic PPO block, independent of the size of hydrophilic PEO block. Hence, the hydrophobicity of the stabilizer is believed to have a major role in stable polymer adsorption onto the hydrophobic drug surfaces by forming high surface concentrations. This was confirmed by the above findings, which showed that the most hydrophobic stabilizer P123 (69 PPO units) demonstrated the smallest nanoparticle size, followed by the medium hydrophobic F127 (65 PPO units), and the largest size was demonstrated by the least hydrophobic F68 (30 PPO units). Hence, the important descriptive factors of stabilizers that enabled better understanding of the effects of the structure of each stabilizer on PS were the stabilizer type, the ratio of hydrophilic to hydrophobic units, and the number of PPO units.

Mentions:
The relationships between the independent and dependent variables were summarized by the model in 3D response surface plots demonstrating the effects of two independent variables at average levels of other variables on the output parameters (Figures 1–3). The results of response surface plots showed that the most effective formulation variables that directly affect the PS of the nanosuspensions included stabilizer type, number of PPO units, weight of stabilizer, and the ratio of hydrophilic to hydrophobic units (Figure 1). The effect of the type of stabilizer on PS can be explained by the response surface plot (Figure 1A) showing that the PS values were low at stabilizer type 1 (Pluronic F127), high at stabilizer type 2 (Pluronic F68), and low at stabilizer type 3 (Pluronic P123). The ratio of hydrophilic to hydrophobic units (PEO/PPO) demonstrated increasing effects on PS moving from 0.55 to 3.05 and finally to 5.07 corresponding to Pluronics P123, F127, and F68, respectively (Figure 1B). However, the increase in PPO units from 30 (F68) through 65 (F127) and finally to 69 (P123) was found to have prominent decreasing effect on the PS, which is consistent with the effects of stabilizer type. Also, the increased weight of stabilizer led to a decrease in the size (Figure 1C). The drug to stabilizer ratio and phase volume ratio were found to have increasing and decreasing effects on PS, respectively (Figure 1D). The decrease in PS with increased levels of phase volume ratio might be due to the formation of more nucleation sites per unit volume of the antisolvent (aqueous phase). This caused the precipitation of less drug molecules per nucleation site and consequently decreased PS.46 Moreover, the decrease in PS with an increased weight of stabilizer could be attributed to the decrease in surface tension, which facilitated the size reduction and stabilized the formed nanoparticles with inhibition of aggregation.27 It is well known that the conformation of physically adsorbed triblock copolymers (Pluronics) depends on the hydrophobicity of the sorbent surface.47 The hydrophobic PPO block anchors to the hydrophobic surface, leaving the PEO chains extending in the aqueous phase, and when the number of the adsorbed polymeric chains is sufficiently high, a brush conformation is formed.47,48 The adsorption of a series of Pluronics on polystyrene colloids was studied to probe the effect of PEO chain length and the hydrophilic/hydrophobic block length ratio on the adsorption characteristics.49 It was found that the surface concentration of Pluronics on polystyrene colloids is determined by the size of the hydrophobic PPO block, independent of the size of hydrophilic PEO block. Hence, the hydrophobicity of the stabilizer is believed to have a major role in stable polymer adsorption onto the hydrophobic drug surfaces by forming high surface concentrations. This was confirmed by the above findings, which showed that the most hydrophobic stabilizer P123 (69 PPO units) demonstrated the smallest nanoparticle size, followed by the medium hydrophobic F127 (65 PPO units), and the largest size was demonstrated by the least hydrophobic F68 (30 PPO units). Hence, the important descriptive factors of stabilizers that enabled better understanding of the effects of the structure of each stabilizer on PS were the stabilizer type, the ratio of hydrophilic to hydrophobic units, and the number of PPO units.

ABSTRACTCarvedilol (CAR) is a potent antihypertensive drug but has poor oral bioavailability (24%). A nanosuspension suitable for pulmonary delivery to enhance bioavailability and bypass first-pass metabolism of CAR could be advantageous. Accordingly, the aim of this work was to prepare CAR nanosuspensions and to use artificial neural networks associated with genetic algorithm to model and optimize the formulations. The optimized nanosuspension was lyophilized to obtain dry powder suitable for inhalation. However, respirable particles must have a diameter of 1-5 µm in order to deposit in the lungs. Hence, mannitol was used during lyophilization for cryoprotection and to act as a coarse carrier for nanoparticles in order to deliver them into their desired destination. The bottom-up technique was adopted for nanosuspension formulation using Pluronic stabilizers (F127, F68, and P123) combined with sodium deoxycholate at 1:1 weight ratio, at three levels with two drug loads and two aqueous to organic phase volume ratios. The drug crystallinity was studied using differential scanning calorimetry and powder X-ray diffractometry. The in vitro emitted doses of CAR were evaluated using a dry powder inhaler sampling apparatus and the aerodynamic characteristics were evaluated using an Andersen MKII cascade impactor. The artificial neural networks results showed that Pluronic F127 was the optimum stabilizer based on the desired particle size, polydispersity index, and zeta potential. Results of differential scanning calorimetry combined with powder X-ray diffractometry showed that CAR crystallinity was observed in the lyophilized nanosuspension. The aerodynamic characteristics of the optimized lyophilized nanosuspension demonstrated significantly higher percentage of total emitted dose (89.70%) and smaller mass median aerodynamic diameter (2.80 µm) compared with coarse drug powder (73.60% and 4.20 µm, respectively). In summary, the above strategy confirmed the applicability of formulating CAR in the form of nanoparticles loaded on a coarse carrier suitable for inhalation delivery.